#include<bits/stdc++.h>

using namespace std;
typedef long long ll;

int main() {
    double top[20] = {2, 3};
    double bottom[20] = {1, 2};
    for (int i = 2; i <= 19; i++) {
        top[i] = top[i - 1] + top[i - 2];
        bottom[i] = bottom[i - 1] + bottom[i - 2];
    }
    double sum = 0;
    for (int i = 0; i < 20; i++) {
        sum += top[i] / bottom[i];
    }
    cout << sum;

    return 0;
}

